Conventionally, electromagnetic flow meters for measuring the flow of fluids, for example, have been used as devices for measuring physical quantities of fluids flowing in the pipe portions. These electromagnetic flow meters have measured flows of fluids using the Faraday's law of induction wherein an electromotive force that is proportional to the speed of flow is induced in the direction that is perpendicular to the direction of flow and to the direction of the magnetic field when an electrically conductive fluid flows across a magnetic field.
Because of this, the electromagnetic flow meters have been structured from detecting portions, which are structured from measuring tubes, electrodes, and magnetic field generating means (such as a coil or a magnet); a converting portion for calculating a flow rate value by performing signal processing on an input signal from the detecting portion, and for displaying the flow rate value on an attached displaying portion, or converting the flow rate value into a corresponding electric current signal for the outside; and a connecting portion for connecting the detecting portion and the converting portion mechanically, and for connecting the power supply lines and signal lines that are connected between the detecting portion and the converting portion. Moreover, typical electromagnetic flow meters are shipped in a form wherein the detecting portion, the converting portion, and the connecting portion are integrated into a single unit, to be attached to a pipe in a work area.
Recently there has been increasing opportunity for the use of battery-driven electromagnetic flow meters (hereinafter termed “battery-type electromagnetic flow meters”), in contrast to the two-wire and four-wire-type electromagnetic flow meters that operate by receiving a power supply from the outside. The battery-type electromagnetic flow meter operates with a built-in battery as the driving source, instead of external power; however, the internal battery is held in a battery case, and is contained in a case together with the converting portion and the displaying portion (within an equipment case).
FIG. 3 is a schematic diagram of the battery-type electromagnetic flow meter. FIG. 3 (a) is a plan view, and FIG. 3 (b) is a side view. In these figures: 1 is a measuring tube (a pipe portion); 2 is a connecting portion that extends from the measuring tube; 3 is an equipment case that is connected to the connecting portion 2, and an internal battery 4 is contained together with the converting portion and the displaying portion within this equipment case 3. In the equipment case 3, the internal battery 4 is held in a battery case 5, and, in this state, the electrical connection is maintained with the electrical circuitry therein.
This battery-type electromagnetic flow meter is installed on a pipe in a workplace for use, but at the beginning of the flow rate measurement of the fluid, the measurement tube 1 is vibrated by the fluid that flows within the measurement tube 1, and that vibration propagates through the connecting portion 2 to the equipment case 3. When the equipment case 3 vibrates, the relative position between the battery case 5 and the equipment case 3 will change, which, in some cases, makes it impossible to maintain the electrical contact between the internal battery 4 and the electric circuitry within the equipment case 3.
In response, Japanese Unexamined Patent Application Publication 2003-151519 (“JP '519”) describes a battery enclosure mechanism that prevents the disconnection of the power supply when there is a physical shock due to dropping or vibration, in a structure wherein a battery box (corresponding to the battery case 5) is contained within a case main unit (corresponding to the equipment case 3).
In the battery containing structure disclosed in JP '519, a contact terminal that contacts the positive electrode of the battery and a conductive spring terminal that contacts the negative electrode of the battery are provided within the battery box, and the battery box is contained within the case main unit so as to be able to slide in the lengthwise direction of the battery, where spring members are provided on the inside of the case main unit so as to press against and hold the ends on both sides of the terminals of the battery box, where the spring constants of the spring members within the case main unit are lower than the spring constant of the spring terminal in the battery box. That is, the spring members within the case main unit have higher elasticity then the spring terminal of the battery box. As a result, when there is a physical stock from the outside, the spring members within the case main unit absorb the shock more readily than the spring terminal in the battery box, securing the supply of power from the battery in the battery box.
However, the battery containing structure disclosed in JP '519 is only effective for vibration in the lengthwise direction of the battery, and has no effect when it comes to vibration in the direction perpendicular to this direction. That is, in the case of a battery-type electromagnetic flow meter, the battery containing structure set forth in JP '519 cannot be used as-is for a device wherein there is the potential for the receipt of a vibration in a variety of directions through vibrations propagating to the equipment case from a variety of directions.
The present invention is to solve this type of problem, and the object thereof is to provide an internal battery-type field device wherein the connection between the battery in a battery case and the electric circuits that are contained in an equipment case is secured, even in relation to vibrations from any given direction on the equipment case.